—Teaching computer architecture is a difficult task, especially to inexperienced students who prefer developing their java programing skills rather than understanding how machine instructions are executed effectively on a silicon black box. Because manipulating electronic components in a classroom is highly complex and complicated, teaching activities used to be aligned to simulation and exercises on paper. During the last 2 years we have developed a set of practical experimentations on FPGA boards. From scratch the students, in twelve 2 hour lessons, build their own processors and execute small programs on them with their own assembler and assembly language. A step by step approach permits the students to understand by design the different concepts of processors that are introduced during the lectures. All the labs are based on intuitive realization of elementary bricks and then combining them like a game of Legos. The results after two years are more than positive and some students have chosen to pursue a Masters of Computer Science with a particular interest in architecture design. The S3 processor can be considered as PBL (Project Based Learning) that covers all revised Bloom's taxonomy levels of knowledge acquisition.